The present invention relates to a method of dispersing carbon black in liquid elastomers. More specifically, the present invention relates to a low shear method for adequately dispersing carbon black in liquid elastomers.
Cured or vulcanized elastomers invariably must be compounded with reinforcing fillers to improve properties such as tensile strength, stiffness, abrasion resistance and tear resistance in order to permit their use for items such as tire tread, tire carcass as well as for hoses, belts and other mechanical goods. One outstanding reinforcing filler for both natural and synthetic elastomers is carbon black.
Heretofore in the field of liquid elastomers, that is, elastomers which are liquids at ambient or slightly above ambient temperatures, carbon black (which has been beaded or pelletized either by blending with water to form water beaded blacks or with glycerin to form glycerin beaded carbon blacks) was incorporated by adding the carbon black to the liquid elastomer and dispersed by the use of very high shear equipment or mixers such as the three roll paint mill. In the mixing of conventional rubbers, shear is generated partially by the rubber or polymer itself whereas in liquid elastomers, such internal shear generating properties are not present and thus carbon black cannot be adequately dispersed by using high shear mixers such as the Banbury, Brabender or the like. High shear equipment such as the three roll paint mill must be used. However, this high shear equipment is expensive, consumes great amounts of power or energy and requires long periods of time to adequately incorporate or disperse the carbon black. Moreover, heat build-up is often a problem and would sometimes scorch or degrade the elastomer. This high shear three roll paint mill is also not readily scaled-up to production capacity.
In the production of conventional rubbers, the vulcanization route briefly involves cutting rubber stock, mixing the cut rubber stock as in a Banbury Mixer, heating the stock via warm-up rolls, either extruding, injecting molding or pressing the stock and then vulcanizing the stock. These many steps, of course, require a high amount of capital as well as several pieces of expensive equipment. On the other hand, the liquid elastomers of this invention, after having been adequately dispersed with oil, carbon black and other compounding ingredients, are still relatively low in viscosity and can be processed and cured in equipment requiring much less energy and capital costs than conventional rubber processing equipment.
A search of the United States Patent Office has not revealed any patents which incorporate carbon black into liquid elastomers by a method similar to or suggestive of the present invention.